1. Field of the Invention
The present invention relates to a biodegradable and bioactive glass-ceramic, and a method for fabricating the glass-ceramic. More particularly, the present invention relates to a biodegradable and bioactive glass-ceramic fabricated by mixing a slowly biodegradable glass-ceramic and a highly biodegradable glass-ceramic in a predetermined mixing ratio wherein the bioactivity is maintained to be constant, and the biodegradation rate is controlled by the mixing ratio.
2. Description of the Related Art
The most widely used bioactive glass-ceramic for artificial bones or bone cements is Cerabone-AW®, of which composition is suggested in Japanese Patent Laid-Open No. 03-131263 (1989). The glass-ceramic composition consists of MgO, CaO, SiO2, P2O5 and CaF2 wherein the weight ratio between the respective components is 4.6:44.7:34.0:16.2:0.5. The glass-ceramic composition is compacted at near 830° C., and oxyfluoroapatite (Ca10(PO4)6(O,F)2) and β-wollastonite (CaSiO3) are consecutively crystallized at near 870° C. Since the glass-ceramic exhibits excellent bone conductivity, it can be directly bonded to bones. In addition, since the glass-ceramic has a high compressive stress of 1080 MPa, a high hardness of 680 Hv, a high bending strength of 178 MPa, and a high fracture toughness of 2.0 MPa·m1/2, it can be used as artificial vertebra and iliac crests, etc. to which a stress is directly applied.
However, since the glass-ceramic is substantially insoluble in a living body, it cannot be completely replaced by bone for a relatively long period of time.
On the other hand, U.S. Pat. Nos. 4,103,002, 4,234,972, 4,851,046, etc., disclose other bioactive glasses. These glasses are highly bioactive, but have a very low mechanical strength. In addition, the glasses are so readily biodegraded that they are limited in the application to artificial bones.
Presently known and commercially available conventional bioactive glasses and glass-ceramics have a satisfactory mechanical strength, but they have a problem that their biodegradation in the body is too fast or too slow.